Hierarchical databases use a parent-child relationship model. In this type of database, data is organized into a tree-like structure that implies a single-parent for each record. This model allows the representation of data in a hierarchy which is very much like a family tree. Each parent can have multiple children, but each child has only one parent (also known as a one-to-many relationship).
The hierarchical database model was one of the first database models, historically used with mainframe computers. In this model, records contain information about their groups of parent/child relationships, similar to a family tree. If we consider a database of employees,each department would be a parent node, and each employee within that department would be a child node of the department.
References: The concept of parent-child relationships in databases is well-established and discussed in various educational resources and forums. For example, Stack Overflow provides explanations of how these relationships work in practice12. Additionally, other resources like phoenixnap.com explain how these relationships are established in databases3.